The invention is based on a device for measuring the mass of a flowing medium. A device has already been disclosed (DE-PS 44 07 209), which has a temperature-dependent measurement element that is accommodated in a measurement conduit that extends in a straight line. The measurement conduit extends in the device from an inlet to an outlet, which is adjoined by an S-shaped deflection conduit. The flowing medium flows from outside into the measurement conduit and then into the deflection conduit, where it flows out again from an outlet opening. The measurement conduit has a rectangular flow cross section, wherein two side faces oriented toward the platelet-shaped measurement element are embodied extending obliquely so that a tapering of the measurement conduit is produced in the flow direction of the medium in the measurement conduit. A top face of the measurement conduit, which extends lateral to the side faces and from which the measurement element protrudes, and a bottom face of the measurement conduit disposed opposite this top face thereby extend in a level or parallel fashion, with a constant distance from each other.
A device equipped with such a measurement conduit is also known from the SAE Paper 950433 (International Congress and Exposition Detroit, Mich., Feb. 27-Mar. 2, 1995, can be inferred from the sectional depiction in the top picture in FIG. 7 on page 108, the measurement conduit and the deflection conduit are essentially comprised of two parts, wherein a part referred to below as the base part, with the measurement element, includes a side face, a top face, and a bottom face of the measurement conduit and the deflection conduit. The other part has only the second side face of the measurement conduit and the deflection conduit and thus constitutes a cover part. The base part and the cover part are preferably made of plastic, for example using the plastic injection molding technique. Because of the tapering shape of the side fades of the measurement conduit, an increasing wall thickness is produced in the flow direction. In the manufacturing, it has turned out that due to the increasing wall thickness, varying cooling speeds and accumulations of material occur, which can in particular lead to hollows in the side faces of the measurement conduit. In a provided mass production of the device, this results in more or less intense variations in the achievable measurement precision of the devices.
The device according to the invention for measuring the mass of a flowing medium has the advantage over the prior art that in mass production, devices with a properly manufactured housing can be produced so that only extremely slight variations in the measurement precision occur. It is also particularly advantageous that by means of the embodiment, according to the invention, of the walls of the measurement conduit, an acceleration of the flow in the measurement conduit can furthermore be maintained, which leads in a known manner to a stabilization of the flow of the medium in the measurement conduit, particularly at the inlet.
Advantageous improvements and updates of the device disclosed are possible by means of the measures taken.
An inclined embodiment of an edge face of the deflection it conduit is particularly advantageous, with which it is possible to further simplify the manufacturing of the measurement conduit and the deflection conduit, wherein a further improvement of the measurement result also occurs.
Furthermore, a flow connection to the external flow in the intake line is provided in the deflection conduit in the form of an opening, by means of which possibly existing residual interferences of a pressure wave in the deflection conduit can be completely eliminated so that a further improvement of the measurement result can be achieved. Furthermore, the device has a considerably reduced measurement signal noise, which can be produced by means of turbulences that occur in the measurement conduit.